hen I was a medical student at P&S in the 1980s, professors did not talk about uncertainty. We talked about differential diagnoses and probabilities, but there was always a sense that doctors knewor were learningthe answers to diagnostic and therapeutic problems. The same message was sent to students at other medical schools.

Nevertheless, there were a few physicians who had begun to question this perspective. One was Dr. Jay Katz, a psychiatrist at Yale University, who argued that doctors brushed aside medical uncertainty. The lack of candor on this issue, Dr. Katz believed, typified what he called the silent world of doctor and patient. Another critic was Dr. Bernard Fisher, a surgeon at the University of Pittsburgh, who rejected the continued allegiance of his colleagues to the traditional breast cancer operation, the radical mastectomy. Believing that surgeons actually did not know whether such an extensive operation was necessary, Dr. Fisher organized the first randomized controlled trials of breast cancer surgery in this country.

Given this history, it is perhaps fitting that the latest controversy over uncertainty in medicine also surrounds breast cancer. In the Oct. 20, 2001, issue of the Lancet, two Danish researchers, Drs. Ole Olsen and Peter Gotzsche, reported that screening mammography did not, as previously advertised, save lives from breast cancer. When Gina Kolata of the New York Times wrote a front-page story in December 2001, near pandemonium ensued. Mammography advocates strongly rebuked the Lancet paper. Critics of screening held their ground, bolstered by the surprising decision of an advisory committee of the National Cancer Institute to withhold recommendation of the test.

To be sure, screening mammography had long been controversial for women under age 50. Since the 1970s, critics had charged that the downsides of mammography, ranging from missed cancers to radiation exposure to unnecessary biopsies of benign lesions, outweighed its modest benefits among such women. But the latest reports also applied to women aged 50 to 70. Almost no one had previously challenged the ability of screening mammography to reduce mortality from breast cancer in this age group by roughly 30 percent.

As were most clinicians, I was surprised by the conclusions in the Lancet. But as a historian who had just written The Breast Cancer Wars, a history of breast cancer diagnosis and treatment in the 20th century, I was not surprised by the ferocious response to the discordant opinions of the Danish researchers. For one thing, to question mammography was to question early detection, which has been the dogma of breast cancer control since the early 1900s.

More importantly, perhaps, the latest challenge to mammography raised serious questions about the medical professions ability to ever definitively prove the value of the test. Drs. Olsen and Gotzsche had based their conclusions on a meta-analysis, a sophisticated statistical review of the eight existing randomized controlled trials of screening mammography. Yet others who had examined the same data had generated the exact opposite conclusion: Screening mammography saved lives. While Dr. Bernard Fisher had been able to prove that radical mastectomy was obsolete by conducting randomized trials, eight such trials of screening mammography had not been able to generate a definitive answer.

I was less distressed than others about the latest mammography controversy. As I discuss in my book, women with breast cancer or at risk for the disease have always benefited more from a frank discussion of medical interventions than from physicians well-meaningbut at times inaccurateassumptions. Knowledge is power, whether or not that knowledge provides patients with definitive answers.

But some physicians regret that the current controversy over screening mammography is being played out on the front pages of newspapers. A full-page open letter signed by 10 prominent medical organizations in the Jan. 31, 2002, New York Times expressed grave concerns that these public debates have already begun to erode the confidence in mammography that has been built up over the past two decades. While we should be careful not to rashly abandon long accepted medical practices, such as mammography, the new reports should stimulatenot stiflediscussion between women and their physicians.

The current uncertainty over screening is hardly limited to breast cancer. Men may now opt for prostate-specific antigen (PSA) testing, which permits the detection of early-stage prostate cancers. Here, too, the jury is out. Some physicians believe that the existing data confirm the tests value and recommend it to their patients. Others believe that PSA testing is unproven and may not even raise the issue. But, as in the case of mammography, men deserve to hear about the current PSA controversy and make informed decisions as to whether they want screening. The same is true for spiral-CT scanning, a new technology currently being touted for the early detection of lung cancer.

It is hard to oppose evidence-based medicine. After all, which patients and doctors want to make difficult decisions based on inadequate information? But when the data indicate a true difference of opinion, physicians need to be frank. Patients can deal with uncertainty. Doctors should do the same.

Dr. Barron H. Lerner is Angelica Berrie-Gold Foundation Associate Professor of Medicine (in the Center for the Study of Society and Medicine) and Public Health (in Sociomedical Sciences). Robin Eisner, editor of In Vivo, provides editorial guidance for Point of View contributions.